The major effort will be to extend the biological and chemical characterization of HL-A alloantigens and to evaluate HL-A antigens in the sera of cancer patients to establish any variation in their qualitative and quantitative distribution. Attempts will be continued to correlate the expression of HL-A antigens with other cell surface markers or in vitro cell activities. To this end sufficiently pure HL-A antigens will be isolated from serum to permit their extensive molecular characterization, including amino acid sequence analysis. Efforts will be made to utilize HL-A xenoantibodies (produced in our laboratory by injection of purified HL-A antigens in rabbits and goats) to develop a sensitive radioimmunoassay to detect HL-A antigens in serum. BIBLIOGRAPHIC REFERENCES: Hoch, J.A., Dierich, M.P., Pellegrino, M.A., Ferrone, S., and Reisfeld, R.A., Distinction between malignant L cells and normal mouse fibroblasts by rosette formation with sheep red blood cells, J. Immunol. 114:1638, 1975. Pellegrino, M.A., Ferrone, S., and Theofilopoulos, A.N., Rosette formation of human lymphoid cells with monkey red blood cells., J. Immunol. 115:1065, 1975.